How do spiders make webs?

18 October 2009

Question

How do spiders build their webs? Are they brilliant mathematicians?

Answer

We put this question to Todd Blackledge, Associate Professor of Biology at the University of Akron:"Surprisingly, despite how elegantly symmetric orb webs are, they don't have a map of the shape of the web. Instead, they have genes that control how they move individual legs as their manipulating silk thread and how to interconnect silk threads. It all starts off with a bridge thread. So a spider can suspend its web in mid air by releasing a very lightweight silk thread until it snags on something such as a tree on the other side of the trail you're walking on. That bridge thread then forms the core of the web. The spider is able to move out and begin to build an outer framework for the web, at the same time as it establishes what are called the radial threads, those you can think of as the spokes on a wagon wheel. And then once this framework is done, the spider then produces a temporary spiral, so it starts at the centre of its web and this temporary spiral acts as a physical guide for the spider to then spin the final gluey capture spiral. And the spider starts at the outside of the web, follows that temporary spiral and essentially paints itself into a corner in the centre of its web. They actually use their legs to measure the distances. So if you watch an orb spider spinning its web, it's reaching out with one set of legs to touch the temporary spiral and then using its hinds legs to then position the sticky spiral. So spacing between rows of silk is going to change as the spider matures and the length of its legs grows longer and longer."

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